Method of making decorative wood panels

ABSTRACT

A METHOD FOR PRODUCING AN OVERLAID DECROATIVE WOOD PANEL WHICH DOES NOT SHOW CRACKS IN ITS VENEER. A GLUING AGENT PREPARED BY MIXING A THERMOSETTING RESIN GLUING AGENT AND A THERMOPLASTIC RESIN GLUING AGENT IN THE RATIO OF ABOUT 1:0.5 TO ABOUT 1:2 IS APPLIED TO A SUBSTRATE WOOD MEMBER. THEREAFTER, A NON-SIZED PAPER IS APPLIED INTO WHICH THE GLUING AGENT FOR PAPER IS ALLOWED TO PERMEATE AND SET TO TOUCH. A THERMAL PRESSING IS GIVEN TO THE PAPER, A GLUING AGENT FOR A DECORATIVE VENEER IS APPLIED THEREUPON, AND THE DECORATIVE VENEER IS FASTENED THERETO.   D R A W I N G

p ,1972 TUTOMU NAKAJIMA EI'AL 3,690,976

METHOD OF MAKING DECORATIVE WOOD PANELS Filed Oct. 23. 1969 2 Sheets-Sheet 1 'FIGI 11\"VE./\"7URS' TSUTOMU NAKAJIMA TADASHI SHAKU aggwr wug ATT'YS Sept. 12, 1972 TUTOMU NAKAJIMA I'AL 3,690,975

METHOD 0F MAKING DECORATIVE WOOD PANELS Filed Oct. 25. 1969 2 Sheets-Sheet 2 ATT'YS United States Patent Ofice Patented Sept. 12, 1972 3,690,976 METHOD OF MAKING DECORATIVE WOOD PANELS Tutomu Nakajima, Osaka, and Tadasi Shyaku, Hyogo, Japan, assignors to Asahi Fancy Plywood Co., Ltd., Osaka, Japan Filed Oct. 23, 1969, Ser. No. 868,767 Int. Cl. B32b 31/12 U.S. Cl. 156-90 1 Claim ABSTRACT OF THE DISCLOSURE A method for producing an overlaid decorative wood panel which does not show cracks in its veneer. A gluing agent prepared by mixing a thermosetting resin gluing agent and a thermoplastic resin gluing agent in the ratio of about 1:05 to about 1:2 is applied to a substrate wood member. Thereafter, a non-sized paper is applied into which the gluing agent for paper is allowed to permeate and set to touch. A thermal pressing is given to the paper, a gluing agent for a decorative veneer is applied thereupon, and the decorative veneer is fastened thereto.

BACKGROUND The present invention relates to a method for producing an overlaid decorative wood panel which does not show a crack in its veneer, more particularly the method for producing a decorative panel by bonding a very thin decorative face veneer layer of a choice wood to the surface of a substrate wood member.

Hitherto a decorative plywood of this sort has been made by strongly bonding a decorative veneer to the surface of a substrate wood member with a gluing agent. But, when the decorative plywood of this kind is used as a wall panel or a ceiling, numerous cracks of about 0.5 mm.1.0 mm. wide and mm.-20 mm. long frequently appear, resulting from differences in temperature, humidity of the atmosphere, and the like. Since the beauty of a decorative plywood is its soul, such cracks seriously detract from its value.

As a solution to this problem, one of the present inventors suggested a method for producing a decorative plywood wherein a woven cloth is put between a substrate wood member and a decorative veneer. Goods made according to this method have received some acceptance. However, this method is relatively expensive because of the use of the woven cloth, and there has been a need for a cheaper method of producing decorative plywood that shows no crack on its surface.

If paper rather than Woven cloth is used, the cost will be reduced. However, previous attempts to put paper between the wood member and the decorative veneer have not been successful. For example, in the past, a gluing agent for paper has been applied to the surface of a substrate wood member, the paper is placed thereon, and then a thermal pressing is applied by means of a heat roll or a flat-faced heating press. The paper can be placed on the gluing agent either while the gluing agent is still moist or after it is dried. Thereafter, a bonding agent for the decorative veneer is applied to the paper, and the decorative veneer is fastened to the substrate wood member by heat or cold pressing. This method has proved unsatisfactory for several reasons. When a thick paper of more than 40 g./m. (grams per square meter), i.e., 0.1 mm., is used, the paper will absorb moisture in the gluing agent and will swell. This will cause wrinkles in the surface of the veneer and detract from its appearance. On the other hand, if the glue is not moist or humid, the bonding agent for the decorative veneer does not permeate into the paper enough because of the air remaining in the paper layers, and the veneer will not be properly secured even if the paper is bonded by thermal pressing. Consequently, an exfoliation will occur in the paper during use.

If a thin paper of the order of 25-40 g./m. is used and if the gluing agent applied on the substrate member, i.e., 0.06-0.1 mm, is humid, the paper lacks firmness in comparison with the aforementioned thick paper and, although expansion wrinkles will be held down by a press, the paper will be resinified so as to nullify the effect of the paper layer as a buffer, thereby defeating the original object of using the paper layer. If the gluing agent is dry, the same problem as discussed with respect to the thicker paper will arise.

When a thin paper of less than 25 g./m. is used, the paper lacks resistance to prevent cracks from appearing in the veneer.

SUMMARY The foregoing problems have been overcome by using a bonding agent for the paper prepared by mixing a thermosetting resin bonding agent (40%-70% resin content) and a thermoplastic resin adhesive 35 %50% resin content) in the ratio of about 1:0.5 to about 1:2. The bonding agent is applied to the surface of the substrate wood member, and thereafter a non-sized paper having a thickness of about 25-40 g./m. is applied. The gluing agent for paper is allowed to freely permeate the paper, and after this gluing agent is set to touch, a thermal pressing is given to the paper. A gluing agent for the decorative veneer is then applied to the paper, and the decorative veneer is placed thereon and thereby fastened to the substrate wood member.

We have found that a variety of papers can be used, such as Japanese mitsumata paper, Manila paper, kraft paper, and cotton paper. However, the thickness of the paper is preferably limited to about 25-40 g./m. If the thickness is less than 25 g. m. the paper does not provide enough of a buffer, neither the swelling nor the shrinkage of the substrate wood member can be neutralized enough by the paper, and cracks cannot be completely prevented. If the thickness exceeds 40 g./rn. the gluing agents for both the paper and the decorative veneer will not permeate sufficiently crosswise into the interior of the paper, as will be explained more fully hereinafter, and it is believed that an exfoliation will take place between papers.

A non-sized paper is preferable to sized paper since with the latter the gluing agent may not permeate completely into the paper.

The gluing agent for the paper is a mixture of a thermosetting resin adhesive and a thermoplastic resin bonding agent. A thermosetting resin bonding agent has good permeability into the paper layer, but if this gluing agent alone is used, we have found that there will be approximately permeability so that when the paper is dried, resinification will result. On the other hand, a thermoplastic resin gluing agent has low permeability. These two adhesives are mixed with each other in order to utilize their permeability into the paper layer and the enhanced activity of the adhesives by a thermal pressing. The adhesives are working to some extent as rivals, and we have found that the most appropriate permeability and activity of the adhesives into the paper layer can be attained in the aforementioned range of ratios of mixture.

The nature of the gluing agent for the decorative veneer is not quite so critical since, because of the mixed gluing agent for paper, it is unlikely that an air layer will be generated or that excessive permeability will result due to the thermal pressing. However, we have found it desirable to use a mixture of a thermosetting resin gluing agent and a thermoplastic resin bonding agent in the ratio of about 1:1 to about1:2.5.

The invention may be better understood by reference to the accompanying drawing, in which- FIG. 1 illustrates a perspective view, partially broken away, of a product made in accordance with the invention;

FIG. 2 is a greatly enlarged sectional view of the upper portion of the article;

FIGS. 3 and 4 are views similar to FIG. 2 but of articles formed by prior methods;

FIGS. 5 and 6 illustrate microscopic enlargements of the cross section of the article illustrated in FIG. 3, FIG. 5 being enlarged 500 times and FIG. 6 being enlarged 125 times;

FIGS. 7 and 8 illustrate microscopic enlargements of the cross section of the article illustrated in FIG. 4, FIG. 7 being enlarged 500 times and FIG. 8 being enlarged 125 times,

FIGS. 9 and 10 represent microscopic enlargements of the cross section of the article illustrated in FIGS. 1 and 2, FIG. 9 being enlarged 500 times and FIG. 10 being enlarged 125 times.

Referring now to FIGS. 1 and 2, a gluing agent 2 for paper is applied on the substrate wood member 1, and a nonsized paper 3 is temporarily placed thereupon with a normal temperature roll while the gluing agent remains humid. The roll pressure should be relatively light so as to serve only to feed the substrate wood member into the succeeding manufacturing process. The non-sized paper is composed of interwound fibers in various densities. Consequently, in the part of the paper where the fibers are interwound slightly, the gluing agent 2 can readily enter into the paper and reach the upper side of the paper on the strength of its own permeability, forming numerous wedges 2a in the paper. In the part of the paper where the fibers are interwound thickly, the gluing agent permeates very little into the paper.

The gluing agent 2 is allowed to dry until set to touch. Thereafter, a thermal pressing is given by means of a thermal roll or a flat thermal press to complete the bonding. Since condensation is slowly progressing during the set to touch of the bonding or the gluing agent 2, the gluing agent for paper has a small fluidity as in a non-pressure condition, and it will harden in a conddition where there is an irregularity in the microscopic permeability into the paper layer.

The gluing agent 4 for the decorative veneer is then applied on the paper 3, and the permeability of the gluing agent 4 will vary according to the air in the paper layer. However, since the gluing agent 2 for the paper is hardened and since there is an irregularity in-the permeability into the paper layer as described, the gluing agent 4 will not permeate much into the portions occupied by the wedges 2a but will permeate into the paper layer in the part where there are no wedges. The gluing agent 4 will thereby permeate to the lower side of the paper layer 3 and form numerous wedges 4a.

Finally, a decorative veneer 5 is placed over the gluing agent 4, and first a cold pressing and then a heat pressing is applied to fasten the decorative veneer to the substrate wood member while the wedges 4a remain crosswise with the lower wedges 2a.

The goods made by conventional methods are shown in FIGS. 3 and 4. In FIG. 3 a gluing agent 12 for paper is applied on the substrate wood member 11, and a paper layer is applied thereon while the glue is humid. The glue greatly permeates the paper, the paper loses its original nature, and a resinification will take place. The veneer 15 is bonded by the gluing agent 14, but the resinjfied paper will not prevent the appearance of cracks in the veneer.

In FIG. 4, the paper 23 is secured to the substrate wood member 21 after drying the gluing agent 22 for the paper. The permeability of the gluing agent 24 for the decorative veneer 25 will thereby be prevented by the air in the paper layer, and the bonding of the veneer remains imperfect.

The character of the bonds obtained in the articles in FIGS. 3 and 4 can be further understood by referring to FIGS. 58. FIG. 5 represents a microphotograph of the cross section of the product illustrated in FIG. 3, the microphotograph showing an enlargement of 500 times. FIG. 6 is a similar microphotograph with an enlargement of 125 times. In FIG. 5, the primed numerals refer to corresponding portions of FIG. 3 indicated by the unprimed numerals. Similarly, the double primed numerals in FIG. 6 refer to corresponding portions of FIG. 3. As can be seen in FIG. 5, the gluing agent 12' for the paper which is applied to the substrate member 11' has completely permeated the paper. The bonding agent 14' for the veneer is placed thereon, and the veneer 15' is secured by the bonding agent 14'. Similarly, in FIG. 6, the gluing agent 12" is seen to permeate the paper and extends from the substrate member 11" to the bonding agent 14" for the wood veneer 15". The bonding agent for the decorative wood veneer and the bonding agent for the paper are permeating through the entire body of the paper. Accordingly, checking or crazing is liable to occur by wane of adhesive and by swelling or shrinkage of wood.

FIGS. 7 and 8 are similar microphotographs for the structure illustrated in FIG. 4, FIG. 7 representing an enlargement of 500 times and FIG. 8 representing an enlargement of 125 times. Referring to FIG. 7 the paper bonding adhesive 22' which is applied to the substrate member 21' and the veneer bonding adhesive 24 which attaches the wood veneer 25' permeate through the body of paper 23' just a little. Accordingly, the paper is liable to break away as at 23a. This can also be seen in FIG. 8, in which the paper bonding agent 22" and the veneer bonding agent 24" permeate relatively little into the paper 23".

FIGS. 9 and 10 represent similar microphotographs of the structure formed in accordance with the invention as illustrated in FIG. 2. Again, FIG. 9 represents a microphotograph of 500 times enlargement, and FIG. 10 represents a microphotograph of 125 times enlargement. Referring to FIG. 9, both the bonding agent 2' for the paper and the bonding agent 4' for the veneer 5' permeate through the paper 3' in the form of wedges. The bonding agents will therefore not cause the break away of the paper, and the paper retains its nature. Similarly, in FIG. 10, the bonding agent 2" which is applied to the substrate member 1" and the bonding agent 4" which secures the veneer 5" are seen to permeate through the paper 3" in the form of wedges.

Products made according to the present invention are free from cracks, since the paper maintains its original nature in spite of being put between the substrate wood member and the decorative veneer. The swelling and shrinkage of the substrate wood member due to changes in the humidity in the atmosphere will be absorbed by the paper and will not directly affect the decorative veneer. On the other hand, exfoliation between papers will not take place, since the gluing agents above and below the paper are spreading out crosswise as well as wedge-wise into the paper layer. As a result, an excellent decorative plywood which is free from cracks at all times can be obtained at a very cheap cost.

The invention may be further illustrated by means of the following example. The gluing agent for paper was prepared by mixing 30 parts of urea-melamine co-po1ym erized resin gluing agent, 30 parts of a vinyl acetate resin gluing agent, and 40 parts of an extending agent. This gluing agent was applied to the substrate wood member in a thickness of about g./m. A non-sized paper of 31 g./m. was placed thereon with the aid of a rubber roll, and the structure was dried for 20 minutes in a drying oven at 40 C. After completing the set to touch, a thermal pressing of 10 kg./crn. was applied at 100 C. for 60 seconds. The gluing agent for the decorative veneer was prepared in the same manner as the aforementioned gluing agent for paper and was applied on the paper in a thickness of 120 g./m. A walnut decorative veneer having a thickness of 0.3 mm. was placed thereon and given a thermal pressing of 10 kg/cm. at 100 C. for 90 seconds. The resulting decorative plywood product was free from any exfoliation in the papers, and the decorative veneer showed no cracks.

Similar results have been obtained using other thermosetting and thermoplastic resins when the ratios of these resins varied in the range of 1:05 to 1:2.

While in the foregoing specification, a detailed description of our invention has been set forth in considerable detail for the purpose of illustration, it will be understod that many of the details herein given may be varied considerably by those skilled in the art without departing from the spirit and scope of our invention.

We claim:

1. A method for producing an overlaid decorative wood panel characterized by the absence of cracks in the veneer comprising the steps of applying to the surface of a substrate wood member of gluing agent for paper prepared by mixing a thermosetting resin gluing agent and a thermoplastic resin gluing agent in a ratio within the range of 1:05 to 1:2, applying a non-sized paper having a thickness of about 0.06 to about 0.1 mm. while the gluing agent is humid, allowing the gluing agent to freely permeate the paper and set to touch, thermal pressing the paper after the gluing agent is set to touch, applying a gluing agent for a decorative veneer, applying a decorative veneer to the gluing agent for the veneer, and thermal pressing the decorative veneer.

References Cited UNITED STATES PATENTS l/1955 Repsher et a1. 156-90 X 1/ 1956 Lindenfelser et a1. 15 6-90 X 

